Electrical musical instrument



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ELECTRICAL MUS ICAL INSTRUMENT Filed March 20, 1946 1l Sheets-Sheet l Nov. 29, 1949 .1. A. oswALD ELECTRICAL MUSICAL INSTRUMENT ll Sheets-She??l 2 Filed March 20. 41946 Nov. 29, 1949 J. A. @SWALD 2,989,497

ELECTRICAL MUSICAL INSTRUMENT Filed March 20, 1946 11 Sheets-Sneet 3 1517 6 affari". Lmj. 25 wald.

Nov. 29, 1949 J. A. OSWALD 2,489,497

ELECTRICAL MUSICAL INSTRUMENT Filed March 20, 15.346 ll SheeiS-Sheet 4 @ff p4 swf( Nov. 29, 1949 J. A. OSWALD ELECTRICAL MUS ICAL INSTRUMENT Filed March 20. 1946 l1 Sheets-Sheet 5 Y 2177165 afd/Zai.

J. A. OSWALD ELECTRICAL MUSICAL INSTRUMENT Nov. 29, 1949` 11 Sheets-Sheet 6 Filed March 20.41946 Nov. 29, 1949 J. A. oswALD 2,489,497

ELECTRICAL MUSICAL INSTRUMENT Filed March 20. 1946 1.1 Sheets-Sheet '7 bja Nov. 29, 1949 J. A. OSWALD ELECTRICAL MUSICAL INSTRUMENT 1l Sheets-Sheet 8 Filed March 20, 1946 Nov. 29, 1949 J. A. oswALD ELECTRICAL MUSICAL INSTRUMENT 11 shams-sheet 9 n x f. f wx wx x /ovH/M. w Wx x n a r @i /ww m Kx W 1 j ,f W wm Y 5% vw %N WW lhl 7 .mJ ww .N M F L.. r P www ww wg. wm Nba m m hl@ Q \N von@ .QQ MM ww f Filed March 20. 1946 Nov. 29, l949 .1. A. oswALD ELECTRICAL MUSICAL INSTRUMENT 11 Sheets-Sheet 10 Filed March 2o, 194e JZ Harney.

Nov. 29, .1949 J. A. oswALD ELECTRICAL MUSICAL INSTRUMENT ll `Smets-Sheet l Filed Maron 2o, 194e Patented Nov. 29, 1949 UNITE? STAT ELECTRICAL MUSICAL INSTRUMENT James A. Cswald, Chicago, Ill., assignor to Cen- Vtral CommercialCompany, Chicago, Ill., a corporation of Illinois Application March 2011946, serial No. 655,835

.9 Claims. 1

This invention relates to electrical musical instruments and more particularlyto keyboard instruments, the playing-keys Vof which are coactive with generators of tone signal voltages and with an electroacoustical translating device forv conversion of signal voltages from selected generators into audible sound for musical expression. In the instant embodiment of my invention, reference is made to a single keyboard asillustrative of a simple but practical and musically useful application of my invention. Reference will be made to only a minimum number of tone frequency or waveform generators, such that for each playingkey of the instrument there will be one'generator individual thereto', Vbut connected in an electrical network for concurrent transmission through separate channels'of dividedr portions of the output wave from said generator, whereby a note of the same pitch can be soundedin response to selective, concurrent actuation of respective instrurnentalities of the instrument, such as stops, playing-keys of one or more keyboards, or the keys of a pedalboard. Theeherein disclosed embodiment of my invention will be sufficient to teach persons trained inthe art in use-of the underlying features of my invention for a great variety of purposes and accompanying increase in the musical possibilities of an instrument of this class.

The pitch of 'organ stops is spoken of, relative to the ordinary pitch, forfexample, of the violin. Taking the open G string of the violin, a note of the same pitch is called -foot tone. But, on the organ, a stopl may be drawn giving the same tone and the same color one' octave higher, called l-foot tone; Similarly, each tone color, in general, may be produced from the same key at (Cl. Sli-1.19)

pitches varyingfrom two octaves lower to two Y octaves higher. 'In exceptional cases,` this may be expandedV to provide Gli-footand l-foot tones.

@n the organ this is accomplished by bringing into use various sets'of pipes,` the total'number of which determines the-'pitch range of the instrument. In a single manual instrument having sixty-one playing-keys and an alternator or wave generator for each individual playing-key, octave coupling by means ofstops is limited, due to the fact that the lowest frequency producedby any generator is approximately 65 cycles per second, the highest frequency being approximately 2093 cycles per second. Obviously, if the range is' to'bc extended either up or down from one or the other of these pitches or both up and down therefrom additional generators will be required. It suffices to say that in most instances, the range will be extended, at least to include a l-foot tone.

An object of my invention is the provision of a simple and dependable system of generators and stops, whereby octavely related generators can be selectively drawn uporrfor concurrent distribution of their output waves through anV electrical network, andsimilarly, concurrently translated into audible sound of two or more pitches of the ages from selected generators in a manner insurthat the divided portions of any selected wave are the same in amplitude.

A still further object is the provision of means in a keyed `instrument employing alternators or generators of tone signal voltages for suppressing noise,` such as key thump or pop heretofore unavoidably resulting in consequence of sudden electron surges when close circuiting said alternators or generators with the input circuit of an amplifier.

My invention, though it may find expression in various embodiments has, common to each thereof, the broad idea ofthe combination of resistances and wave generators which are so connected. in an electrical network that proportionalityin amplitude of divided portions of the output of any generator is effectively secured regardless of the number of said portions being transmitted at the same instant to a translating device, and whereby, when any generator is close circuited with said translating device, there will be such attenuation of saidportions that extraneous frequencies heretofore resulting in objectionable noise will be extinguished.

My invention is illustrated in the accompanying drawings in which Figures 1 to 4, inclusive, are diagrams illustrating the broad form of my invention; Figures 5 to 13, are respective parts of a composite network embodying my invention; Figure i4 is a diagram employed as a reference key to the sequence of Figures 5 to 13 to form a composite of saidfigures; Figure l5 is a perspective view of one of the electric switches, and Figure i6 is a longitudinal, section through said switch showing an application thereof to a playing-key.

A comprehensive understanding of the principle and modus operandi of the main characterizing features of myinvention will be had upon referring to the schematic graphs and circuits shown lat Figures l to 4, inclusive of the accompanying drawings. In Figure l, curve a is typical of the gradual attack and' decay of a pipe tone. Curve b is typical of the percussive attack of a Due to the 'fact that both the ear drum and the cone or diaphragm of a loud speaker have-inertia and resilrience, theA attack of curve c is characteristic of sound, which; tothe ear is represented by curve dandis responsible for-an unpleasant thump or pop "similar to that which ytypifies sound emitted from anypercussive instrument.

At Figure 2 a simple voltage divider circuit is illustrated. In this figure voltage E is impressed between points l and 2 by battery B. By Ohms law, the voltage V which will be measured between 3 and 4 will be If R2 is a xed resistance and RI a resistance which is variable from zero to some nite value, V then becomes a function of Rl. We will assume that RI is connected by some mechanical arrangement to a depressible operating key K in Figure 3 in such manner that gradual descending motion of the key gradually increases the resistance of RI from zero when the key is fully elevated and at rest to some finite value when the key is depressed. Thus, it becomes apparent that by proper selection of the taper of resistance Rl or by proper mechanical linkage between the key and Rl or by a combination of the two, that any growth of voltage can be attained for a linear movement of the key and that the exponential rise of curve a, Figure 1 may be attained, thereby suppressing the objectionable thump or pop that otherwise would be experienced.

If we substitute a source of audio signal for the iattery of Figure 2 and the playing-key of an organ or other keyboard instrument for the key K of Figure 3, we can let the curves of Figure 2 represent signal voltage (RMS) or tone intensity delivered to the amplifiers. The simple circuit of Figure 3, however', has other restrictions placed on it for use in an instrument circuit. For example, while the larger RI becomes relative to R2 more signal is delivered and the less the loss in the circuit, it is necessary, however, to restrict RI to a low value compared to R2 in order that the generating source shall not be subject to too wide a variation in load between key up and key down conditions and also in the case where a given tone frequency is used on more than one key-(octave couplers or more than one manual), and to prevent robbing between these two or more keys. In addition, since it is necessary to combine the outputs of several keys to form a single channel, isolating resistors must be used to prevent the grounding of the common channel by any key in the group which is not depressed. In this same connection the isolating resistor must be high compared to Rl and also to the impedance of the common channel if robbing is to be prevented.

Figure 4 shows a practical circuit using this method of keying when S is the audio frequency source, PI an output path connecting the plate circuit of source S to a common conductor X. Conductor X is connected to the input circuit of an amplifier A, the latter grounded at G. Connected in series in said path Pl are xed resistors R2 and R3. Connected across said path at the juncture point between said resistors R2 and R3 is a variable, key operated resistor RI, the same grounded at G2. Resistor R2 will be hereinafter referred to as an isolating resistor and R3 a protective resistor. Resistor R2 constitutes an element of a potential divider, and is connected in parallel with a plurality of similar xed resistors R2 in respective signal output paths P2. R3 are paths to common conductor X from respective audio frequency sources which will be hereinafter shown and referred to in complete detail.

As Rl is increased from zero to its maximum value by operation of its associated key the signal applied to the grid of the amplifier A will rise smoothly by any curve selected to a maximum value. 'Ihis maximum signal will be maintained until the key is released and at that time the signal will be smoothly reduced to zero as the key rises. As previousiy stated, the curve of the attack and decay can be made to have any form desired by proper selection of resistance taper and mechanical linkage.

In the accompanying drawings, Figures 5 to 13, inclusive, are continuations of an electrical network, which, except for my additions, refinements and improvements, is similar to the invention shown and described in the patent to Merwin J. Larsen, No. 2,403,090, July 2, 1946. In carrying my invention into practice, I have so improved and refined certain features of the Larsen invention that the system, as a whole, functions in a greatly superior manner and with attainment of new and highly desirable functional results. Particularly are these refinements and improvements directed to dependable means for suppressing noise heretofore resulting from sudden electron surges when close circuiting the waveform generators of the instrument with the input circuit of an electroacoustical translating system.

In the instant embodiment of my invention, footage stops are an important contribution to the art of electric organs of the class employing generators of waveforms of voltage pulses having the tone frequencies of octavely related musical notes. In instruments having more than a single manual, several factors must necessarily be considered to the end that the range of musical possibilities shall be improved and results attained which are more nearly comparable to the organ than heretofore possible with instruments of the prior art. Such factors include the necessity for securing proportionality in amplitude of divided portions of the output waveform from any single generator when the generator is drawn upon for concurrent use of the same frequency in different parts of the instruments gamut. As distinguished from the pipe organ and its two or more sets of pipes for as many footage stops, my invention employs a single set of waveform generators from any single generator of which, a waveform of voltage is adapted to be concurrently distributed through different channels according to the number of times the same waveform is used in the rendition of a musical score.

In instruments employing more than one manual and a pedal keyboard, it frequently is necessary to draw upon a single generator for many uses at the same time of the same tone frequency. In fact, the output wave from said generator might possibly be used concurrently a great many times at each manual and at the pedal keyboard in the playing of a musical composition. Instruments employing but a single manual are less complicated, yet, even in this simple instrument, the same frequency might also be used concurrently a great many times if the range of the instrument extends above and below the range of a sixty-one note manual. An example of this would be an instrument employing stops for coupling octavely related frequencies. The herein disclosed invention is that of an instrument of this type. I merely elect this form of disclosure as it entails less complications and neither encumbers this description nor the drawings.

In the pipe organ, proportionality is not a factor for consideration in that footage stops depend entirely upon separate ranks of nues, the flues of each rank functioning separately and apart from the ues of any other rank, such, 'for example, 16' vflues`8' iiues; 4' flues and 2' flues, lto which can be added such mixtures as 16' reeds, 8 reeds and 4' reeds.

As distinguished from a pipe organ, an electric organ must necessarily be reduced to a very minimum cf parts. Such instrument-must be readily portable and compact and otherwise characterized, that its cost of production is low compared to that of a pipe organ, yet such instrument must have musical possibilities more or less comparable to pipe organs. In "the instant embodiment of my invention'use is made of a single generator for each note in the instruments gamut. These generators are substantially the same throughout theentire system. Each generator produces an output signalor waveform of voltage which is rich in harmonics. Any individual generator can be drawn upon for concurrent transmission thr'ough'the network of the output signal from said generator. The'number of times the same Waveform is used at any vinstant will, of course, depend upon the use it is to serve. In order that mathematically correct additive effects can be had, division of voltage from a respective generator must be such that all divided parts thereof that are being concurrently transmitted through the network, shall be of equal amplitude.

The term frequency employed herein shall meanan audio tone signal-regardless of the precise waveform. A more useful Waveform for every purpose of my invention, however, is one which is rich in its harmonic composition so as to include a large number of frequencies which are true harmonics of the fundamental.

Referring now to Figures 5 to r13, inclusive, which, when conjoined according to the key chart (Figure 14) form a composite organ network, it is noted that twenty-seven generators CI to D3, inclusive, are 'shown as sources of tone signal voltages covering a range of pitches Afor more than a single octave of notes. A single playing-key is shown at Figure 16 and it will suffice merely to say that each individual generator will be actuable from a respective playingkey for selective conduction of voltage through the network and resultant activation of aloud speaker. While I have shown'a single playingkey, I point to multiple electric switches Ki to K2'l, inclusive, as indicative of playing-keys Ito 21 of a short organ keyboard of vsixty-one Vplaying-keys. These generators may be of the form shown in Patent No. 2,410,883, November 12, 1946, to Larsen et al., or they may comprise any well kno-wn system of generators 5or alternators for producing complex waveforms .of signal voltages at the tone frequencies of diferentnotes of the chromatic scale.

The plate circuit of each waveform generator is provided with an output lead L having parallel high resistive branch paths PI and P2, such that the Waveform of output voltage from said .generator can be concurrently transmitted through said network for desired use thereof at the'same instant. In each of these branch paths is -a series resistance P3 of 1 megohm, the purposeof 'said parallel resistances being to provide a voltage divider by means of which portions of the output Voltage from a generator will be of the same amplitude when said generator is drawn upon for concurrent use of the same frequency. In series with resistance P3 in eachbranch path Pl, P2, is a resistance P4, also of one megohm.' n

As the ordinary pitch of the organ is 8ft. playing-keyKl y'equals v'cyclesfperfsecond; playingkeylKZ equals 69 cycles per second, etc., to and inclusive'of playing-'key K6! equals 2093 cycles per second, va tone an octave i above playing-key Kl will have a frequency of`131cycles per second and will b'eassociated With--playing-key Ki3. While my disclosure is conned vto'means for producing 4-foot and 'S-foot tones which may be played separately `or together, obviously, this rangecan beprojected either upwards or downwards, limited vonly by the'total number offrequencysources employed and the range of frequencies available from said sources.

It will be apparent to persons-trained in the art that limitations upon the extent of octave coup-ling orability toobtain given footage tones is connedtothe number of generators employed and the range of frequencies'produced by said generators. For example, an instrumentihaving but sixty-one generators covering a' range of frequencies from 65 cycles per second to 2093 cycles per second will not permit octave coupling beyond a limited range of the keyboard. Increasing'the number of generators to provide both higher and lower frequencies obviously increases the coupling range and in those cases Where rthe frequency range has been suiiiciently extended, 2', 16', 32', and 64' tones can beproduced and the instrument played at 'any one or all of these pitches. In the instant example, eight foot tones are available from top'to bottom ofthe keyboard. Four foot tones, however, are limited to that section of the keyb0ard,'the playing-keys of which are coactive with generators producing frequencies an octave higher than theordinary eight foot range of said keyboard.

The following reference chart isi'ndicative of the range of frequencies produced by the twentyseven generators herein shown and has-been extended to include frequencies associated with playing-keys an octave above playing-key K2?, thereby providing for the'purposefof this disclosure a useful range of both eight and four foot tones.

Octavely related frequencies keys 1-27-8 ft. cmd 4 ft. range 8 ft. 4 ft. Key L 65 C. P. S. 131 C.P.zKey'lI-B Key 2----- 69 C.P.S- V188 C. P. S.=Key i4 Key 3 73 C.P.S. 147 C. P. S.=Key i5 Key 4 78 C. P S. 156 C. P. S.='Key i8 Key 5 82 C.P.S. 165 C.'P.S.=Key IT Key i' 87 C.P.S. 175 C. PSS-:Key I3 Key 1 92 C.P.S. 185 C.P.'S.=Key'|9 Key 8 8 C.P. 196 C. P. S.=Key 29 Key 8 164 GPS. 208 C'.P.S.=`='Key 2! Key l C. P. S. 220 C. P. S.=Key 22 Key i l 117 C.P. S. 233 C.P.S.=Key 23 Key 2 123 C. P. Si. 247 C. P. S.=Key 24 Key i3 131 C`. P. S. 262 C.P.S.=Key'25 Key EL 139 C. P. S. 277 C. P. S.=Key 26 Key i5 147 C.P.St 294 C`.'P.S.=Key 21 Fey lb 156 C. P. S. 311 C. P. S.=Key 28 Key H C. RS. 330 C.P.S.=Key 29 Key l8 175 C.P.S. 349 C. P. S.'=Key 30 Key |9 185 C. P.S. 3701 C.`P.S.=Key 3i Key 28 195 C'. P. S. 392 C. P. S.=Key 32 Key 2i---" 208 C. P.S. 415 C.P.S.=Key`33 Key 22 220 C. P. S. 440 C. P.S.=Key'3' Key 23 233 C. P. s. 46e C.P.s.=Key 35 Key 22 247 C. P. S. V494 C. P. S.=Key 3S Key 25 1 262 C. P. S. 523 C.P.-S.=Keyf31 Key 26 277 C. P. S. 554 -C. P. S.=Key 38 Key 2l' 294 C.P.St 588 C'.P.S.=Ke'yf39 Referring to Figures to 10, inclusive of the drawings and taking for example, generator GI=98 cycles per second, it is noted that connected across branch path Pl is a resistance R20. Playing-key K8 associated with this gen erator operates adjustable contactors CII! and CI I, the former coacting with resistance R and the latter with resistance R2I connected across path P2 from generator G2=196 cycles per second, an octave above GI. Paths P2 from generators CI to BI, inclusive, connect to a common ground GII). Adjustable contactors CIU and CI I for each playing-key are connected to ground GII. Signal voltage from generator GI is conducted to a collectorl Bld which is common to generators producing output signals, the tone frequencies of which are 92; 98; 104; 110; 117; and 123 cycles per second, constituting one complete key group.

The waveform of voltage from generator G2=196 cycles per second is conducted to a collector BI I which is common to generators, the tone frequencies of which 135; 196; 208; 220; 233; and 247 cycles second and when coupled to generators common. to collector BIO give four foot tones. This constitutes another key group. Each individual collector' of the set of ten collectors herein shown is provided with a common output conductor LIB which is connected in the network in a manner to be described presently. These conductors are respectively connected to input leads Gl to Girl of Wave lter apparatus, detailed reference to which will be made later in this description.

Similarly, all generators embodied in the re maining key groups connected to respective collectors, each provided with an output conductor LID, While I make provision for ten groups only eight thereof are connected in the quality control system as shown at Figures 1l, 12 and 13.

Connected across each ci said output conductors LIQ is a variable resistive switch, RIE. Twenty of such switches are shown, such that there is a gang consisting of ten switches for eight-foot tones and a similar number for fourfoot tones. These switches are adapted to be controlled by the customary organ stop tabs (not shown) All switches associated with pitches corresponding to an eight foot tone will be connected as a common gang ci switches for simultaneous operation from a single stop tab. All switches associated with pitches corresponding to four foot tones will be similarly connected for simultaneous operation. It understood that in any case where the range of footage tones is increased above the number here-in shown, each individual playing-key will have its switch number correspondingly increased. According, as these stops are drawn, the pitch of the organ is changed. ln the instant case if both stops are drawn tones in octave relation will speak upon depressing a single playing-key in that section of the keyboard in which provision for coupling is made. Should all stops be in their retired positions, the key-switches circuits are broken and no audible sounds can be produced from the keyboard.

Referring to Figures 9 and l0 of the drawings, input leads GI to GI@ from the respective key groups are each thereof individual to a preassigned input division or section of a quality control system to be fully described later in this general description of my invention, At this point, however, and as each input lead of a given key group is a common conductor for signal voltages 8. at frequencies lying ln a, predetermined band o1' frequencies, it is necessary to note that these leads are arranged in numerical or successive order of the playing-keys of the organ, such that lead LI from the rst or extreme bottom group of playing-keys is individual only to that group. In like manner is this true of each of the remaining groups of keys of which ten such groups constitute the total number of groups employed in this example of my invention, the tenth group comprising seven keys. For an organ embodying a short keyboard consisting of a total of sixtyone playing keys, the frequency of each tone associated Awith a given playing-key and the grouping of particular playing-keys will be fully understood upon reference to the following chart:

When simultaneously depressing two or more playing-keys, each of which is connected to a generator for concurrent use of divided portions of the same output frequency, leads LII) through which these portions are transmitted will connect to a preassigned one of the input leads Gl to GIO. In each of said leads LIIJ is a resistance LII of suflicient value to prevent robbing during simultaneous conduction of frequencies from respective generators or when portions of the same frequency are being concurrently conducted from a single generator.

Key grouping approximate frequencies 8 it. range o1 :Key 1:65

Ctlll:Key 2:69

gl Group 1 to Tube T1 El :Ke 5:82

F1 :Key 6:87

A? :ggg lz Group 2 to Tube T2 A#1:Key 11:117

B1 :Key 12:123

C2 :Key 13:131

Cit2=Key 14:139

D2 :Key 15:147

DzzKey 16:156; Group 3 to Tube T3 Group 4 to Tube T4 Group 5 to Tube T5 Group 6 to Tube T6 Group 8 to Tube T8 B4 :Key 48:988

(-15v 1=Key 49:1046 C=Key 50=ll09 D5 =Key 51:1175 Dr5=Key 52:1245 E5 `="Key 53:1319 F5 :Key 54:1397 Fg5=Key 55:14.80 G5 :Key 56:1568 G5=Key 57=l66l A5 =Key 58:1760 A5=Key 59:1865 B5 =Key 60:1976 C5 =Key 61:2093

Group 9 to Tube T9 Group to Tube T10 The output of each key group isiinpressedon the grids of tubes T|,.T2 L Tl@ respectively. These tubes may be twin triodes as indicated or separate triodes or pentodes. The function of these tubes is to divide and isolate the Vgroups from each. other and also to provide separate isolated output channels for apurpose presently to appear. For examplethe grids of TiV arein common, and the cathodes are inl common, whereas one plate of one triode is connected'to a low-pass filter circuit to activate the filter LPI; The plate of the other triode passes through decoupling resistance 35 toa common lead I-I'I' and also through resistance 3l which, ink connection with capacitance I4, suppresses the higher har-l monies of the waveforms in the'group concerned to aA lower level. The output across capaci-- tan'ce I4 passes through decoupling resistance to a common leadV I I6. Thus, it follows that output from TI may pass through Va plurality ofisep arateoutput paths. Similar provision is 'made for the other tubes T2, T3 TIII."V Thefiiltering capacitances I4, I5, I6 2t,4 however, dif-.- fer in value in order to 'provide 4essentially .the same reactance at the mid-frequency.'ofltheir corresponding key. groups. The magnitudes of these reactances, for example,v are substantially thesame as the vmagnitudes o-f the resistances .31. `l"In"thevcombined Figures l1, i2 and x13, ywherein tenY high vacuum tube isolators TI, T2, etc., lare shownfor as many individual groups GI,`G2,= etc. of playing-key switches, the Vcommon cathodes ofthe odd'numbered` twin triode tubesarecon'- nected to ground by resistive capacitive circuits, including resistance AI2 in series between ground and said common cathode'sand capacitances. I3 inshunt between saidresistances and ground, the even' numbered tubes ,being :coupled-:to saidrresistances at'theterminals thereof which connect with said cathodes. Y i e rf ,f The output from common lead IIS-is amplified byfa conventionalI resistance-coupled stage .TI-2, the output of which isfed toconductive lead-X2 of the mixing network M. -v The .outputrof commonV leadY |51-, carriesawvaveform richin har-- monies from resistances in the secondbutput branch from thel plate of therighthand-triode `of stage TI, and leads to a conventional amplifier 6 stage TI3, thefoutput ofwhich is divided... part going to the mixer through. lead. X3 landthe otherr part going toan amplifier stage TI4, which supplies-a group of `band-pass lters and thence to mixingnetworkM..

`These band-pass filters are vdesignated BPI, BP2 BPB-and.. as shown, theyare coupled to. common-input lead |39 through decoupling resistancesl, I4 Ti.. Each of said filters has a separate output lead to the mixer, which leads are designatedX4, X5 '..X8. The .characteristicsof these band-pass filters will be dis-- cussed hereinafter. v The outputs of all of.theaforementionediowpass filters pass to a common lead ||8 through respective decouplling-resistances l39, 40 .48, inclusive. The common lead I I8 carries the substantially sinusoidal waves of frequencies vcorresponding to the fundamental components of the vrespective notes in the instruments gamut. The output of lead IIB is amplified through the conventional amplifier stage Til, the output of which passes to the mixing network via a lead The function of the mixing network is to pro.- vide a means of selecting any number of out-v puts from the various leads XI, X2 X8 at predeterminedamplitudes. This is accomplished by means of decoupling resistances 93,94 |.I2 which connect either singly or in groups to simple stop switches designated SI, S2 SII'. Whenr the switches are on, the main amplifier |20 activates the speaker 12|. When any timbre controlling stop switch is in the o position, the contact lever connected to its associated resistance group 93 I|2 is grounded through common lead ||3 in order to prevent cross talk.

The amplier input resistance |I4 is necessarily much lower than any of the decoupling resistances 93, 94 ||2, in order to prevent robbing amongst the stops. Likewisethe defA coupling resistances just mentioned should be higher than the output impedances associated with said common leads XI, X2 X8, although the relative proportioningin this case will depend upon the particular choice of qualities set up for the whole system. .k

Low-pass filter LPI is designed to start attenuf ating at F2 which has a frequency of 8.7.3 cycles per second. By this means there is no compo# nent having a frequency between 87.3 cycles and 130.8 cycles which ever enters the filter, thus providing a wide margin allowing for attenuation. The lowest frequency mentioned .outside. of the fundamental note range associated with this group, namely 130.8 cycles, corresponds to the frequency of the second harmonic produced by the lowest note C2 in this particular group. If, for example, the key groups should comprise l2 notes each, the second harmonic of the highest-note in that group would be attenuated adequately. withV a simple low-pass lter, but the second harmonic of the lowest note in that particular group would be attenuated but slightly as it is so close to the frequency of the fundamental of the highest note in said group. It therefore follows that with l2 or more notes in a group a change in tone quality takes place from one end to the other. within said group. By means of the aforementioned lesser number, say 6 notes to a group, the difficulties aforementioned are not encountered and a simple low-pass filter can be employed that will function in a highly satisfactory manner.

It is, of course, understood that the modusoperandi of all others of the low-pass filters herein employed is substantially the same as that of filter LPI just above explained.

The purpose of the band-pass filters is to provide a series of formant regions of a number and spacing along the frequency spectrum adeouate to provide a choice of tone qualities when used by themselves and/or with other sources associated with the mixing network. The particular band-pass filters employed herein have a rather high coefficient of coupling of between four tenths and five tenths which permits arelatively wide band of frequencies to pass through. The coils 83, 84, 85, 35i and 8,1 areair-core, wound coaxially, each coil having an inductance of approximately 300 millihenries. The capacitances 88, 90, Sl and 92 are adjusted experimentally to provide the desired band-pass region. For example, the mid-frequencies of the bands em ployed are 500 cycles for band-pass lter BP-l 800 cycles for band-pass filter BP-3; 1500 cycles for band-pass filter BP-4 and 2200 cycles for band-pass filter BP-5,

Each of these would reinforce predominantly over a range extending approximately half an octave, although the attenuation outside the band is not sharp. One of the filters herein called a band-pass filter, namely, filter BP-2 is simply a loaded resonant circuit having a more narrow pass region which resonates at approximately 1400 cycles. The terminating resistances i3, 19 82 determine to a large extent the sharpness or Q of the filter. These outputs pass to tl e aforementioned leads X4, X5 X8 which sup ply the mixing network.

The waveform of any single note which appears on the output of the common lead il@ is essen-- tially the same in its harmonic constitution irrespective of the note played. Because of the aforementioned selective filtering action of the resistances 31 and capacitances lll, iii 20, this waveform is predominantly the fundamen al together with a large series of rapidly 'tapering higher partials. This waveform appears amplified on lead X2 which supplies the mixing netM work. It should be noted here that successive filtering by resistance-capacitance networks would require a very large array of sections be fore a more fiute-like tone quality would be possible which would compare with the lov/pass filters. This follows because, in capacitancea resistance networks higher partials are suppressed, yet are not completely obliterated as with the low-pass nlters just described. The waveform of any tone on the common load on the other hand, is richer in harmonic output as the only integrating action employed is that of capacitances l, 2, I0 which are associated with their respective key groups Gl, G2 G10. If the individual tone generator output wave-- form is rich in harmonics as the case in the generator disclosed in said Patent No. 2,410,883, then the waveform appearing on lead H7 is still moderately rich in its harmonic composition. This waveform appears amplified on lead which connects to the mixing network and is also the same waveform which appears further amplified on the common leao H9 which supplies the aforementioned band-pass filters.

No claim is made to the features herein set forth and pertaining to the patent to Merwin J. Larsen, No. 2,403,090, it being merely intended that it shall serve to meet all statutory requirements for a full and complete disclosure of a practical embodiment of my invention. Regarding reference herein to multivibrators or relaxation oscillators as tone frequency sources, it shall also be understood that these equally serve my purpose and likewise are a statutory reference to one known means for practicing my invention. Any other well known type of waveform generator might possibly be substituted therefor with equally satisfactory results.

No claim is made to the aforementioned quality control and mixer systems shown and described herein apart from use therein in the described combination with those new and novel features which form my contributions and improvements, namely, those changes and embodiments including the various circuit constants such (l) paralle] resistive conductive paths common to preassigned tone frequency generators and fundtioning to enable conduction of respect fe por tions of signal voltage along different paths for use simultaneously according to selective use given stops, and whereby, and incident to their use in the environment herein shown, said re spectve portions of said signal voltage are equal amplitude; (2) resistive switches in sha t with the respective conductive paths for sunn pressing noise otherwise occurring and result from sudden electron surges when closing keying switches.

In a system of tone generation wherein waveforms of signal voltages are changed by a sys*4 tem of filtering, to provide waveforms followingV the wave patterns of various timbres, 'the highest measure of efficiency of such systems can be tained only in those cases where extraneous fre quencies are eliminated and excluded from the input of the amplifier as otherwise the wave patterns sought to be produced by the process oli filtering will not be as predetermined.. The re sultant tones will be unclean or marred. My sistive switches functioning as herein set forth are therefore electrically coactive with said filter system to the end that new and highly beneficial results are assured and tones produced whichv are much closer approximations to tones of given. timbres. Noise which heretofore has blurred re sultant tones is also effectively suppressed. percussiveness characteristic to electric organs is eliminated by progressively increasing and deAw creasing the keyed resistance, and while this doesnot function precisely according to the characteristic attack and decay of tones produced by a pipe organ and therefore is not a means for controlling the attack and decay of tones, said keyed resistances are highly dependable and, in a di tion thereto, are inexpensive by reason of eh. nation of costly time controlled devices in which the attack and decay of tones is a function of time, namely, the time to charge and discharge a condenser. My invention functions merely to termine the amplitude of the wave being conducted through the network of the system according to the depth or" depression of a playing-key on the velocity of the key. Should the key be pressed to a fixed depth between two passible ex.n tremes, and this position maintained, the amplitude will remain constant. The player, however.. has control of this situation as the amplitude can be increased by further depression of the key or it can be diminished by removing pressure there from. These are found to be advantages, however, rather than disadvantages.

A multiple switch mechanically designed to function as aforestated comprises a strip 50 of Bakelite or other well known electrically insulating material formed on one side with sensibly identical grooves 5I, 5|, each terminating at its front end in a fixed contact element 52 adapted to be connected across a tone frequency trans.- mission channel of the electrical network herein shown and described. Each of these grooves is provided with a carbonaceous coating substance so applied that the resistance is of a variable value such that it increases in a direction away from said xed contact. Connected to ground active with each groove is a rectilinear spri contacter 53 which is urged to a position in allelism with the groove so as uniformly to gage the carbonaceous coating in said groove. A spring 54 coacts With said springy contacter to hold same uniformly against said coating and in nyielding''erigagcrrient'@with said'iiiedcon ac le Vment. *Each springy'contactor has a`1foot piece'55 and;A as shown`v atfFi'gure 16;` sam"is in"-coact ive relation to the back end of playing-key' 5'6','-wher`- by upon depressingv said key, said springy contactor will gradually peel off of said carbonaceous coating, thereby-progres'sivelyvarying the resistance from a zero value to whatever may be a predetermined maximum 'value ofsaid resistance.

A multiple switch designed asherein shown and described? is so characterized'that itv may be made of minimum width, to adapt itself to playingkeys'V of customary width at their back ends. Such switches can also'be'm'ade in' gangs or assemblies. each gang or assembly designed for anoctave of playingkys... The three elementV` oscillators shown`h'e'r'einas generators are employed mainly'l for the purpose Vof simplicity,` yet this type of'oscillator' canbe used with equal success as my invention is not dependent upon a specic type of oscillator. An oscillator of the three element type is disclosed in U. S. Letters Patent No. 1,791,319, of February 3, 1931, to F. E. Miller, and would serve my purpose when used in the manner herein stated.

Resistances P3 and P4 are each thereof one megohm. Resistances RIS and LII are each thereof one-half megohm. Blocking condensers C in the output paths L from the respective generators may be of any value calculated to prevent passage of direct current to the wave filtering apparatus, and to maintain approximate constant reactance to the signal voltage.

What I claim as my invention is:

1. A musical instrument comprising a keyboard; an electrical network having an electroacoustical translating system; a plurality of generators producing signal voltages at tone frequencies for a range of more than one octave of notes of a musical scale, said network having a plurality of transmission channels for and common to each individual playing-key of said keyboard and to assigned octavely related generators of said plurality of generators; and means for effecting selective activation of said translating system in response to tone signal voltage from one or more octavely related generators common to playing-keys depressed at any instant, said means including an electric switch in each channel of said plurality of channels common to a respec- 'I tive playing-key, and respective, selectively actuable gangs of electric switches connected in said network and with said transmission channels so that, and in response to close circuiting of the switches of any gang of switches, signal voltages from selected generators will be transmitted through selected ones of the aforementioned channels for activation as aforestated of said translating system.

2. In an octave coupler for electronic organs employing a work circuit, a plurality of sources respectively producing complex tone signals at the frequencies of notes of the chromatic scale, and a keyboard providing a playing-key for cach note in said scale; said coupler comprising mechanism actuable as desired for conducting to said work circuit signal voltage which is the sum of separate signal voltages in octave relation produced by preassigned ones of said sources and including, in combination, a plurality of output paths from each separate source of said plurality of sources, each of said paths having resistances in series, variable resistances common to and controlled by preassigned playing-keys and respectively connected to output paths of octavely related sources, each variable resistance having a terminal connected to a respective one o'fsaid paths at the juncture point betweenthe" series resistances therein, and selectivelyactuable' de"- vices enablingfconduction of said signals'to said work circuit upon actuation of yselected playing keys, the aforementioned sources arranged" rin groups, such that the sources of eachl separate group respectively provide a predetermined band of frequencies, each of said groups of 'sources having an output conductor common only to the sources of that group. *l

3. An octave coupler as setforth'inclam'? wherein a tone filter system'is connected with the output conductors of said groups; `l

4. An octave coupler as set 'forthin cl'aim'2 wherein a tone filter system is connected with the output conductors of said groups and a mixer is connected to the filter system for combining the outputs of different filters of said filter system.

5. In a coupler for electronic organs employing a work circuit, a plurality of sources respectively producing complex tone signal voltages at frequencies embracing more than an octave of notes of the chromatic scaie, and a keyboard providinga playing-key for each note, said coupler comprising mechanism actuable as desired for conducting to said work circuit signal voltage which is the sum of separate voltages produced by preassigned ones of said sources, in combination with a plurality of output paths from each separate source, and selectively actuable devices enabling the aforementioned conduction of said signal voltages to said work circuit upon actuation of selected playing-keys, the aforementioned sources arranged in groups such that the sources of each separate group respectively produce a predetermined band of frequencies, each of said groups of sources having an output conductor common only to the sources comprising that group.

6. A coupler as set forth in claim 5 wherein a tone filter system is connected with the output conductors of the respective groups of said sources.

7. A coupler as set forth in claim 2, wherein a tone lter system is connected to the output conductors of the respective groups of said sources and a tone filter system is connected in common to all of said conductors.

8. A musical instrument comprising a keyboard; an electrical network having an electroacoustical translating system; a plurality of generators respectively producing signal voltages at tone frequencies for a range of more than one octave of notes of a musical scale, said generators arranged in groups such that the outputs of each separate group thereof are at tone frequencies corresponding to the vibration frequencies of given sequentially related notes of said musical scale; and comprise frequencies lying in a given band of frequencies; a system of stops interposed in said network between said translating system and said generators and in which assigned ones of said stops are connected to generators whose outputs have a given frequency relation to each other; a plurality of keying circuits for and common to each separate playing-key of said .keyboard and actuable by said key to effect transmission of the outputs of given generators to said translating system upon drawing one or more of said stops; means electrically coactive with said system of stops for isolating from each other frequencies lying in the different bands of frequencies, and a wave lter system interposed between said isolating means and said translating system.

9. In an electronic keyboard musical instrument, a translating device, sources producing complex audio signals at tone frequencies for more than an octave of notes of the chroma-tic scale; a plurality of collectors, each separate collector connected to predetermined ones of said sources such that each separate collector is individual only to sources producing complex audio tone signals at the tone frequencies of notes as sociated with a given number of sequentially related playing-keys of said keyboard, each of said collectors having an output conductor, connected with said collectors, and mechanism including keying circuits, actuable by said playing-keys and connected to said sources for conduction oi the outputs therefrom, Wave filtering means For repeating the outputs from said sources as outputs having predetermined harmonics above the undamental frequencies of the rst named outputs, a. system of stops for selectively coupling the outputs of sources associated with given playingkeys with the outputs of sources associated with others of said playing-keys and for eecting transmission of the coupled outputs to said translating device.

JAMES A. OSWALD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

